This invention relates in general to vehicle suspension systems and, in particular, to a suspension system especially useful for a four-wheel, two-axle articulated tractor scraper.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a vehicle suspension system for use with a four-wheel, two-axle earthmoving scraper combination for dampening bouncing, pitching and rolling motions encountered during operation.
Articulated wheel or tractor scrapers are used for many applications in the construction industry wherein it is necessary to transport heavy loads of material such as dirt and rock over terrain from one location to another, such as in levelling or filling construction or highway sites. Such wheel or tractor scrapers comprise a two-wheel tractor portion and a two-wheel trailer portion which are articulated about a combined draft and steering coupling or hitch formed between the tractor and trailer. The two units are interconnected by a yoke attached to the trailer which is pivotally mounted on a king pin coupling of the tractor. The tractor scraper is steered by turning the tractor portion with respect to the trailer portion about a vertically disposed articulation pivot axis formed by the interconnection through the use of hydraulic jacks connected between the two portions of the vehicle.
In operating articulated vehicles such as tractor scrapers, it is frequently necessary to allow the tractor and trailer portions of the vehicle to tilt relative to each other about a longitudinal axis extending through the vehicle. Such tilting or rolling is necessary to keep all of the vehicle wheels in contact with the operational surface when travelling over uneven terrain to prevent the loss of tractive power. However, the amount of tilting or rolling movement between the tractor and trailer portions of the vehicle must be controlled in order to maintain vehicle stability. While a limited amount of rolling or tilting of the two portions of the vehicle relative to each other is desirable within predetermined limits, such roll or tilt must be controlled.
In addition to roll or tilt between the tractor portion and the trailer portion of the tractor scraper, bouncing or pitching movement is frequently encountered. Such movement is believed to result from the resiliency of the tires and the weight of the scraper trailer which is suspended between the front and rear wheels of the combination and frequently occurs during hauls at relatively high vehicle speeds. Due to the large size and weight of the tractor scraper, and of the loads transported by it, ordinary shock absorbers or vibration isolators are impractical to resolve the problems created by such bouncing or pitching movement. Such bouncing or pitching movement is uncomfortable and potentially dangerous to the machine operator and, due to the large shock loads imparted by the bouncing trailer portion, can result in damage or failure of structural parts of the vehicle, particularly those closely associated with the load carrying body.
Various attempts have been made to resolve or control the rolling, bouncing and pitching conditions encountered in tractor-trailer combinations. Systems such as disclosed in U.S. Pat. No. 1,990,731 and co-pending application Ser. No. 749,318, filed Dec. 10, 1976, and entitled "Articulated Vehicle Tilt Limiting Apparatus", have attempted to resolve the tilt or roll motion problem through the use of various mechanical linkage coupled between the hitching assembly of the trailer portion and the frame of the tractor portion. Such mechanical linkage permits relative tilting or rolling movement between the two portions of the articulated vehicle within predetermined limits, and then forms a solid connection between the two units when the limits of the rolling condition have been reached.
Many attempts have been made to resolve the bouncing and pitching problems associated with tractor-trailer units. For example, attempts have been made to utilize a separate tractor drive wheel axle frame pivotally connected to the tractor main frame to allow for vertical movement of the tractor drive wheels relative to the frame. In U.S. Pat. No. 3,865,205, there is disclosed such a separate drive wheel axle frame which is pivotally connected to the front portion of the tractor main frame to extend rearwardly to a position beneath the hitch assembly. It is the object of such a coupling arrangement to obtain better weight distribution by permitting the vehicle engine to be mounted on the rear portion of the tractor unit and to allow the vehicle operator to be positioned forwardly of the engine for increased visibility.
In U.S. Pat. Nos. 3,118,686 and 3,549,168 a separate tractor drive wheel axle frame is pivotally connected to the tractor main frame and extends rearwardly to permit the tractor drive wheels to move vertically relative to the tractor main frame. Liquid containing devices are located between the tractor drive wheel axle and the tractor main frame for cushioning bouncing or pitching movement.
Another example of the use of separate frames is disclosed in U.S. Pat. No. 3,845,833 wherein a pair of tractor drive wheel axle supporting suspension arms are pivotally mounted at their rear ends and extend forwardly toward the front portion of the tractor. A pair of ride cylinders, which extend above the tractor side rails, are used to absorb the vertical deflections of the tractor drive wheel axles.
While each of these patents disclosing apparatus attempting to resolve the problems associated with bouncing and pitching movement may have been somewhat successful, such structure does not provide for controlling the rolling or tilting conditions between the tractor and trailer portions of the articulated vehicle.